Hello Harriette, its not an Electric Ray its a Yellow Stingray. They are often found under docks in the shade - a good reason for not wallking around under docks. The Electric Eels are a similar size but have a stubby short tail with an additional dorsal fins on it.
Harriette, have a look at a Paul Humann Reef Fish book and you'll see the difference. Many Dive Shops have a copy as it is excellent. The photograph of the Yellow Stingray isn't the best as they are much more yellow and Green as in your photo.
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